Frequently Asked Questions
Interpreting your Dyno Graph
Trying to understand a dyno graph for the first time can some times be confusing. Let’s try to clarify some things. A typical dyno graph from Axcelerated Motorsports will show you horsepower, torque, and the Air to fuel ratio that was recorded during the run. The graph has an X axis and a Y axis. The Y axis runs vertical and X runs horizontal. You will always find the horsepower and torque on the Y axis. The X axis is at the bottom of the graph and almost always represents RPM, sometimes speed if a good RPM signal was not available. An easy way to tell the horsepower and torque curves apart are to look closely at the two. Horsepower always starts on the low side of the graph and peaks toward the end. The torque curve will start out higher up earlier in the RPM range and gradually drop off. A really nice torque curve will actually be flat and hold steady through out the RPM range.
Why should I get a baseline dyno test?
Having a baseline dyno test done before any modifications will give an accurate starting point to measure the horsepower and torque gains of the new modifications.
Why Did I make the same/less power after I did all this work?
This is a common question, with many answers. I will assume that both dyno tests were done on Dynojets. Comparing a Dynojet run to another manufacturer’s dyno will not give you an accurate comparison. The first thing to do is compare the conditions and the correction factors. All of Axcelerated Motorsports Dyno runs include the conditions of the day on the “numbers” format page. The first thing to do is to compare the conditions of the 2 days. Obviously, if you have one test conducted on a 60* day and one on a 90* day, it isn’t going to be an honest comparison.
After reading the last paragraph, you maybe thinking, isn’t that what the correction factor is for? To correct for differences between run conditions? Yes, but it is primarily used to correct for differences between runs during that same dyno session, on the same day, on the same dyno. It corrects for the ever changing barometric pressure, water in the air and of course temperature.
On the graph, or “numbers” page you will see the correction factor. It may be abbreviated “CF”. There are 3 commonly used corrections factors. Axcelerated Motorsports uses the SAE correction factor. It is the correction factor developed by the Society of Automotive Engineers, and most commonly used throughout the industry. The SAE CF will apply it’s own conditions to the run. Another commonly used CF is the standard or “STD”. The standard correction factor is an optimistic version of SAE, meaning it corrects to better weather conditions. The third CF is “uncorrected”. As it states there is 0 correction applied and is the actual horsepower and torque figures.
Once again if you look at the data on the “numbers” page or in the run notes you will see the correction factor. An example would be CF=1.01 SAE. This is the correction factor for what I would call a bad day. Let’s say this car made 300hp at the wheels uncorrected. To obtain the SAE correction for this day it multiplied 300 X 1.01 to get 303 rwhp. On a good day the CF might be .99 and the Rear wheel horsepower would be corrected to 297 rwhp. Keep in mind that was only an example. In a perfect world that same car that made 300 hp on a bad day should make slightly more on a good day.
I compared my runs and I still don’t know why I am making less power. Could the dyno be off?
No. One of the best attributes of a Dynojet dyno is the accuracy and repeatability of their inertia dynos. Dynojets are individually calibrated by their drum mass at the factory. This calibration is not user adjustable, so no “fudging” of numbers can occur. This type of design leaves virtually no other variables to skew horsepower figures. Due to regular maintenance on our part those variables are non existant. We take our accuracy seriously!
Unfortunately no car is as repeatable as a Dynojet Dyno. There are too many variables. Here is a list I will elaborate on
- Tire pressure. Low tire pressure will cause drag
- Tire/ Wheel change. Bigger wheels and tires have shown as much as a 10 hp loss on the dyno
- Stuck Brake Caliper or parking brake. Creates drag and less horsepower
- Oil weight. Heavier weight oil will cause more drag. Also oil not up to temperature, including trans and gear oil.
- Air to fuel ratio has changed.This is a big deal when comparing runs so check it out!
The above apply to all cars, below is for late model EFI cars.
Ignition timing has changed slightly. Late model EFI cars have many different spark tables that dictate spark based on feedback from other sensors, vehicle load, engine conditions, environment, etc. These tables are add up to come up with final spark. This can be a major variable since a 2 degree change in spark advance can mean a major power difference.
To further complicate matters, a new modification lets say heads for example may change the vehicles calculated load. Since now it can breathe better it’s efficiency has increased. So let’s say before the headers, at 5500 RPM the calculated load was .75. The spark table at this point was commanding 28* of spark advance. Now with the new headers, calculated load is now .80 at 5500 RPM. The spark table at .80 is commanding 26* of total spark advance. So basically you just lost 2 degrees of timing at 5500 RPM. The spark table has to be changed to optimize the new combination. Time to have it tuned!
I had my car dynoed at another shop, and now at yours after making some changes. I have 2 dyno results that are significantly different than what I expected. What is going on?
The first step here is to determine if both dyno tests were conducted on the same machine. Our Dyno is a Dynojet 248H high inertia dyno. All Dynojet Dynos are supposed to be accurate to + or – 1%. If both tests were run on a Dynojet, one factor is ruled out. There is no way to correlate a Mustang Dyno a Dynocom, or any other dyno’s result to a Dynojet. Some say to add or subtract a percentage but it is totally untrue.
Check if both sheets use the same correction factor. there are 3 commonly used, SAE, standard, and uncorrected. The correction factor adds a correction to the dyno results based on the temperature and barometric pressure. SAE is the correction factor that Society of Automotive Engineers uses. Standard is a more “optimistic” version of SAE using a lower temperature and pressure. Uncorrected is with no correction factor applied.
The correction factor is mainly used to correct between runs. Since temperature and barometric pressure change through the course of the day, the correction factor eliminates this variable. The correction factor is not able to make up the difference from a dyno run on a 95 degree day compared to a 60 degree day.
Axcelerated Motorsports uses the SAE correction factor. The information recorded contains the correction factor, temperature, and barometric pressure.It can be found on the dyno run “numbers” format page.
As an example, a car with 300 rear wheel horsepower uncorrected on a really bad weather day, would correct to 306 rear wheel horsepower, with a correction factor of 1.02.
Where do I find my PCM catch code?
You can find the catch code for your PCM in a few places. You are looking for a combination of letters and numbers in bold. Older vehicles will have a 3 digit code while later vehicles have a 4 digit code. In most 2000 and newer vehicles it will be on small white sticker located in the driver’s door jam even with the dash. Older vehicles you will have to locate the PCM and read it off of either the connector at the front or the J3 cover at the back of the computer. Once you have the PCM code, this code can be entered directly into our Advantage 3.0 software to create a custom tuning file. The PCM code can also be retrieved using an SCT flash device such as the XCalibrator 3.
2005 to current Mustangs can find it on the PCM next to the battery.
My car is running really bad, it needs to be tuned?
All too often the customer believes the tune is the problem. More often the problem is a defective sensor, part installed incorrectly, mechanical issues, or a combination that was not designed to work together. Fouled plugs, bad wires, bad gas, grounds all cause driveability issues that may mimic a tuning issue. Very rarely tuning will solve major driveability problems.